1. Field of the Invention
The present invention relates to a battery. More particularly, the present invention relates to a battery and battery housing configured to accommodate externally-applied pressure in a safe manner, wherein a cap portion can be bent in a predetermined direction when the battery is subjected to a transversely-applied pressure, in order to increase a margin of safety against potential short circuits.
2. Description of the Related Art
It is common for portable devices, e.g., video cameras, portable phones, laptop computers, PDA's, and other light weight multi-function devices to employ batteries, including secondary batteries, as a source of electric power. Types of secondary batteries include, e.g., nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, lithium secondary batteries, etc. The lithium secondary battery, in particular, is commonly employed due to its rechargeability, large capacity and compact size. The lithium secondary battery also exhibits a high operational voltage and a high energy density per unit weight, making it increasingly popular for the latest portable electronic devices.
FIG. 1 illustrates an exploded perspective view of a conventional battery. Referring to FIG. 1, a conventional battery may include an electrode assembly 112 having a positive electrode plate 113, a negative electrode plate 115 and a separator 114. The battery may further include a housing to enclose the electrode assembly 112, the housing including a can 110 for receiving the electrode assembly 112 and an electrolyte, and a cap assembly 120 for tightly sealing an upper opening 110a of the can 110.
The electrode assembly 112 may have the separator 114 wound between the positive electrode plate 113 and the negative electrode plate 115. A positive electrode tap 116 may be coupled to the positive electrode plate 113 and may protrude from an upper end of the electrode assembly 112. A negative electrode tap 117 may be coupled to the negative electrode plate 115 and may protrude from the upper end of the electrode assembly 112. The positive electrode tap 116 and the negative electrode tap 117 may be spaced apart by a predetermined distance and may be electrically insulated from each other. The positive electrode tap 116 and the negative electrode tap 117 may be made of metal, e.g., nickel.
The can 110 may be made of, e.g., aluminum or an alloy thereof, and may be formed by, e.g., a deep drawing method. The can 110 may have a substantially flat bottom surface.
The cap assembly 120 may include a cap plate 140, an insulation plate 150, a terminal plate 160 and an electrode terminal 130. The cap assembly 120 may be associated with a separate insulation case 170, and may then be coupled to the upper opening 110a of the can 110 so as to tightly seal the can 110.
The cap plate 140 may be made from, e.g., a metal plate, and may have a size and shape corresponding to those of the upper opening 110a of the can 110. The cap plate 140 may have a hole 141 formed therethrough at a center portion thereof. The hole 141 may have a predetermined size for receiving the electrode terminal 130.
The cap plate 140 may also have an electrolyte injection hole 142 formed therein in a suitable location, e.g., offset to one side. The electrolyte injection hole 142 may have a predetermined size and may be sealed by a sealing means 143. The electrolyte injection hole 142 provides for electrolyte to be injected through the cap assembly 120 after the cap assembly 120 is coupled to the upper opening 110a of the can 110. After injection of the electrolyte, the injection hole 142 may be sealed.
The insulation plate 150 may be made from an insulation material and may be attached to the lower surface of the cap plate 140. The insulation plate 150 may have a hole 151 formed therethrough corresponding to the hole 141, such that the electrode terminal 130 may pass through the hole 151. The insulation plate 150 may also have a receiving recess 152 formed in a lower surface thereof, in order to receive the terminal plate 160.
The terminal plate 160 may be made of a metal, e.g., a nickel alloy, and may be attached to the lower surface of the insulation plate 150. The terminal plate 160 may have a hole 161 formed therethrough corresponding to the hole 141, such that the electrode terminal 130 may pass through the holes 141, 161. The electrode terminal 130 may make contact with the terminal plate 160, e.g., along a contact region at the periphery of the hole 161. Accordingly, the electrode terminal 130 may pass through the holes 141, 151 and 161 and may be electrically connected with the terminal plate 160 while being electrically insulated from the cap plate 140 by a gasket 146 and the insulation plate 150.
The negative electrode tap 117, which is coupled to the negative electrode plate 115, may be welded to a side of the terminal plate 160. The positive electrode tap 116, which is coupled to the positive electrode plate 113, may be welded to a side of the cap plate 140 opposite to the negative electrode tap 117. Alternatively, the negative electrode tap 117 may be welded to the cap plate 140, and the positive electrode tap 116 may be welded to the terminal plate 160. Suitable welding methods may include, e.g., resistance welding, laser welding, etc. Of these, resistance welding may be particularly suitable.
The electrode terminal 130 may have the gasket 146 mounted thereon. The gasket 146 may be made of any suitable insulating material including, e.g., the material used for the insulation plate 150. The gasket 146 may be any suitable form, including, e.g., tubular, annular, flat with a hole defined therethrough, etc. The electrode terminal 130 may be inserted, along with the gasket 146, into the hole 141, such that the electrode terminal 130 is insulated from the cap plate 140.
The electrode terminal 130 may be connected to the negative electrode tap 117, and thus to the negative electrode plate 115, or it may be connected to the positive electrode tap 116, and thus to the positive electrode plate 113, so as to operate as a negative or positive electrode terminal.
The battery illustrated in FIG. 1 may be a conventional lithium secondary battery. Battery designs for the latest portable devices may take advantage of the lithium secondary battery's high energy density to provide small form factor batteries, e.g., thin batteries having an elongated, rectangular shape. However, such designs may have weak battery housings, i.e., the battery may not be able to withstand impact or externally applied pressure. In particular, if the battery is subjected to impact or pressure, the electrode assembly contained in the battery housing may be deformed due to deformation of the can. This may, in turn, result in internal defects such as an internal electric short circuit between the electrode plates. Such defects may have serious results, including fires and explosions of the battery.
FIG. 2 illustrates a generalized perspective view of a compressed conventional battery housing. In particular, FIG. 2 illustrates a conventional battery housing that has been compressed by a force Fa applied in a transverse direction, i.e., applied to opposing sides of the can 110 in a direction normal to the longitudinal axis b. Referring to FIGS. 1 and 2, when the battery is deformed by this transversely-applied force Fa, as is done during compression safety tests, the substantially flat bottom surface of the can 110 may deform inward and upward. Similarly, the substantially flat top surface of the cap assembly 120 may deform inward and downward.
The deformation or caving-in of the can 110 bottom may apply pressure to the electrode assembly 112 contained in the battery housing. In particular, it may force the electrode assembly 112 upward and against the cap assembly 120. This may result in the upper portion of the electrode assembly 112 coming into contact with various elements of the cap assembly 120, possibly causing an internal electric short circuit between the electrode plates and subsequent fire or explosion of the battery.